JP4197254B2 - Production of acrylic acid by heterogeneous catalytic partial oxidation of propane - Google Patents

Abstract

Acrylic acid is prepared by heterogeneously catalyzed partial oxidation of propane by a process in which the steam content of the reaction gas starting mixture is reduced in the course of the process.

Description

  The present invention relates to a process for the production of acrylic acid by heterogeneous catalytic partial oxidation of propane in the gas phase, wherein a reaction gas starting mixture containing propane, molecular oxygen and at least one diluent gas is heated at an elevated temperature. General chemical formula I:

［式中、
M^１は、Te及び／又はSbを表わし、
M^２は、Nb、Ta、W、Ti、Al、Zr、Cr、Mn、Ga、Fe、Ru、Co、Rh、Ni、Pd、Pt、La、Bi、B、Ce、Sn、Zn、Si及びInを包含する群からの少なくとも１種の元素を表わし、
ｂは、０．０１〜１であり、
ｃは、＞０〜１であり、
ｄは、＞０〜１であり、かつ
nは、（I）中の酸素とは異なる元素の原子価及び度数によって決定される数である］の多金属酸化物物質上に導き、この際、プロパンを部分的にアクリル酸に酸化させる。

[Where:
M ¹ represents Te and / or Sb,
M ² is, Nb, Ta, W, Ti , Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Ce, Sn, Zn, Si and Represents at least one element from the group comprising In;
b is 0.01-1;
c is> 0 to 1,
d is> 0 to 1, and
n is a number determined by the valence and frequency of an element different from oxygen in (I)] leading to the partial oxidation of propane to acrylic acid.

  Processes for the preparation of acrylic acid, an important monomer for the production of polymers by heterogeneous catalytic partial oxidation of propane with multimetal oxide materials of the general chemical formula I are known (eg DE-A10111933, DE-A10051419, DE -A10046672, DE-A10033121, EP-A1090684, EP-A962253, EP-A895809, DE-A19835247, EP-A608838, WO00 / 29105 and WO00 / 29106).

  The common features of the theory shown in the state of the art and the results achieved show that the combination of significant amounts of water vapor in the reaction gas starting mixture is advantageous both for the catalytic activity and the selectivity of acrylic acid production. That is.

  However, the disadvantage of this method recommended in the state of the art is that the process for the gas phase catalytic oxidation of acrylic acid yields a product gas mixture, not pure acrylic acid, from which acrylic acid must be separated. It is.

In a typical process, the product gas mixture of the heterogeneously catalyzed gas phase partial oxidation of propane to acrylic acid, in addition to the sub-components of the unreacted propane, for example, propene, acrolein, CO _2, CO, acetic acid and propionic acid But also contains components that are used together as a diluent gas, such as water vapor from which acrylic acid is to be separated to obtain a pure product.

  Based on the outstanding affinity of acrylic acid to water (the superabsorbent used in baby diapers is a polymer based on acrylic acid), more water vapor is diluted by gas phase oxidation The more they are used together, the more the cost of the separation problem becomes.

  In addition, the presence of an increased amount of water vapor promotes undesired propionic acid production as a by-product, which is even more difficult to separate from water vapor due to its similarity to acrylic acid. is there.

  Therefore, from the propane, which can satisfy the catalytic activity and selectivity of acrylic acid generation, although it does not require the use of steam as a diluent gas at all or only in a reduced range. A heterogeneous catalytic partial oxidation process to acrylic acid is advantageous.

  Thus, to produce acrylic acid by heterogeneous catalytic partial oxidation of propane in the gas phase, a reaction gas starting material containing propane, molecular oxygen and at least one diluent gas is generally used at elevated temperatures. Formula I:

［式中、
M^１は、Te及び／又はSbを表わし、
M^２は、Nb、Ta、W、Ti、Al、Zr、Cr、Mn、Ga、Fe、Ru、Co、Rh、Ni、Pd、Pt、La、Bi、B、Ce、Sn、Zn、Si及びInを包含する群からの少なくとも１種の元素を表わし、
ｂは、０．０１〜１であり、
ｃは、＞０〜１であり、
ｄは、＞０〜１であり、かつ
nは、（I）中の酸素とは異なる元素の原子価及び度数によって決定される数である］の多金属酸化物物質上に導き、この際、プロパンを部分的にアクリル酸に酸化させる方法が発明され、この方法は、反応ガス出発混合物の組成を、方法の実施中に少なくとも１回変更させ、反応ガス出発混合物中で、反応ガス出発混合物中に含有されるプロパンのモル量に対して、変更前に含有される希釈ガス水蒸気のモル成分が、変更後より少ない量であるようにすることを特徴とする。

[Where:
M ¹ represents Te and / or Sb,
M ² is, Nb, Ta, W, Ti , Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Ce, Sn, Zn, Si and Represents at least one element from the group comprising In;
b is 0.01-1;
c is> 0 to 1,
d is> 0 to 1, and
n is a number determined by the valence and frequency of an element different from oxygen in (I)], wherein propane is partially oxidized to acrylic acid Invented and this method changes the composition of the reaction gas starting mixture at least once during the performance of the method and in the reaction gas starting mixture relative to the molar amount of propane contained in the reaction gas starting mixture. The molar component of the dilution gas water vapor contained before the change is smaller than that after the change.

  The basis of the process according to the invention is, surprisingly, that the multi-metal oxide material of general formula I is in the reaction gas starting mixture for a certain operating time, relative to the propane contained in the reaction gas starting mixture. First, when a certain component of water vapor is used in combination, and subsequently this component is reduced, in the presence of an increased amount of water vapor as a diluent gas in the catalytic gas phase oxidation of propane to acrylic acid, It is an invention that retains its ability to produce acids with enhanced activity and selectivity. That is, even after reducing the water vapor component in the reaction gas starting mixture, the heterogeneous catalytic gas phase oxidation of propane under otherwise unchanged operating conditions is the case where the heterogeneous catalytic gas phase oxidation is permanently It proceeds with a higher selectivity for acrylic acid production than would be done with less water vapor components in the mixture. This description also applies when the reduction of the water vapor component is carried out to the point where the reaction gas starting mixture no longer contains water vapor after the reduction.

Typically, in the process according to the invention, the reduction of the water vapor component is at least partly adjusted by an increase in the components of the dilution gas that are different from the water vapor and can be used together in the process according to the invention. However, this adjustment need not be performed. Such other diluent gas, in particular, molecular nitrogen, carbon oxides, e.g., CO and CO _2, but similarly, noble gases, for example, a He or Ar. Propane itself falls under this as a diluent gas as well. In this case, propane is used in a superstoichiometric amount relative to the amount of molecular oxygen used in the process according to the invention.

  Typically, a mixture of the aforementioned dilution gases is used. This is usually inert in the process according to the invention. That is, it is chemically unchanged in practice with the method according to the invention.

  Of course, in the process according to the invention, the molar reduction of the water vapor component can be adjusted completely by the equivalent increase in the molar component of the inert diluent gas different from the water vapor, or rather can be overcompensated. In the process according to the invention, it is advantageous to use molecular nitrogen as a water vapor substitute.

  The process according to the invention is typically carried out at reaction temperatures of, for example, 200 to 550 ° C., or 230 to 480 ° C. or 300 to 440 ° C. Of course, in the process according to the invention, the temperature before and after the reduction of the water vapor component may be the same. However, the temperature may be lower or higher after the reduction of the water vapor component than before the reduction of the water vapor component.

  The operating pressure (absolute) may be less than 1 atm, 1 atm or greater than 1 atm in the method according to the invention. Typical operating pressures according to the invention are 1.5 to 10 bar, often 1.5 to 4 bar. The operating pressure may be kept constant or changed during the method according to the invention. That is, the operating pressure may be greater or less than before the reduction of the water vapor component according to the present invention.

  Of course, within the scope of the process according to the invention, the necessary changes according to the invention of the composition of the reaction gas starting mixture can also be carried out several times, for example periodically in succession. That is, after a certain operating time with a reduced water vapor component, the water vapor component in the reaction gas starting mixture can be raised again for a certain time and then lowered again.

  As oxygen source, pure oxygen as well as air or oxygen-enriched or oxygen-poor air can be used for the process according to the invention.

The propane to be used in the process according to the invention has no particularly high requirements regarding its purity. Propane containing propene as an adjunct can also be used in the process according to the invention. The composition of the reaction gas starting mixture of the process according to the invention typically varies within the following range (molar ratio):
Propane: oxygen: H ₂ O: other diluent gases = 1: (0.1-10) :( 0-50) :( 0-50).

The ratio is
1: (0.5-5): (1-30): (0-30)
Is advantageous.

  According to the present invention, the ratio is in the range of A = 1: (0.1-10) :( 0.1-50) :( 0-50) and before the reduction of the water vapor component, After the decrease, it is advantageous that B = 1: (0.1-10) :( 0-30) :( 0-30).

  Advantageously according to the invention, the range A comprises a molar ratio of 1: (0.5-5) :( 2-30) :( 0-30), and the range B has a molar ratio of 1: (0.5- 5): (0-20): (0-30) are included.

  This is especially true when molecular nitrogen is mainly used as another diluent gas. During the application of the composition range A of the reaction gas starting mixture, the reaction temperature in the process according to the invention is preferably between 250 and 550 ° C. and during the application of the composition range B of the reaction gas starting mixture, according to the invention. The reaction temperature in the process is likewise preferably from 250 to 550 ° C.

  In other respects, the method according to the invention may be carried out in the same way as described in the state of the art to be evaluated. That is, the catalyst bed may be a solid bed, a moving bed, or a vortex bed.

  At this time, the multi-metal oxide substance I to be used according to the present invention may be used as such (for example, crushed into powder or strips) or formed into a molded body and used in the method according to the present invention.

  The preparation of the multimetal oxide material I suitable for the process according to the invention may be cited from the prior art evaluated at the outset. Depending on the manufacturing method applied, the structure of the resulting multi-metal oxide is rather amorphous (eg as described in WO00 / 29105 and WO00 / 29106) or rather crystalline (eg EP-A 608838, EP-A 962253, EP-A 895809 and DE-A 19835247).

In this case, the production usually produces a finely divided, preferably finely mixed mixture from the source of the elemental constituents of the multimetal oxide material (starting compound) at standard pressure (1 atm), as well as possible. Subsequently, it is carried out by changing to an active oxide by heat treatment under an atmosphere showing oxidative (eg air), reductive, inert (eg N ₂ ) or reduced pressure. However, it is of course possible to use the multi-metal oxide material I produced by the hydrothermal method of DE-A10033121 in the method according to the invention.

  The shaping of the multimetal oxide material I into a catalyst shaped body suitable for the process according to the invention can be carried out, for example, as described in DE-A 10118814 and DE-A 10119933.

According to the invention, as the multimetal oxide material I, those in which M ¹ = Te are advantageously used. Furthermore, multimetal oxide materials I where M ² = Nb, Ta, W and / or titanium are advantageous for the process according to the invention. Advantageously, M ² = Nb. The stoichiometric coefficient b of the multimetal oxide material I to be used according to the invention is preferably 0.1 to 0.6. In a corresponding manner, the dominant range of the stoichiometric coefficient c is 0.01 to 1 or 0.05 to 0.4, and an advantageous value for d is 0.01 to 1 or 0.1 to 0. .6. Particularly advantageous multimetal oxide materials I to be used according to the invention are those in which the stoichiometric coefficients b, c and d in the formula are at the same time as described above. Other stoichiometric coefficients suitable according to the invention are those published in the specification of the prior art cited at the outset.

  Furthermore, in the method according to the invention, the X-ray diffractogram has diffractive reflections h and i, the vertices at the diffraction angle (2Θ) are 22.2 ± 0.5 ° (h) and 27.3 ± 0. A multimetal oxide material I which is .5 ° (i) can be used advantageously. At this time, the half width of the diffraction reflection may be very small or may be extremely excellent as well.

  In the method according to the invention, the X-ray diffractogram has a diffraction reflection k in addition to the diffraction reflections h and i, the vertex of which is 28.2 ± 0.5 ° (k). I is particularly advantageous.

Among the latter, according to the present invention, the diffraction reflection h is the strongest intensity in the X-ray diffraction diagram, has a maximum of 0.5 °, and the half widths of the diffraction reflection i and the diffraction reflection k are simultaneously ≦ 1 °, In addition, the intensity P _k of the diffraction reflection _k and the intensity P _i of the diffraction reflection i satisfy the relationship 0.65 ≦ R ≦ 0.85, where R is an expression:
R = P _i / (P _i + P _k )
The strength ratio defined by is again advantageous according to the invention. The X-ray diffractogram of this multimetal oxide I advantageously does not show a diffractive reflection whose maximum is 2Θ = 50 ± 0.3 °.

  Of these multi-metal oxide materials I, it is advantageous for the process according to the invention that 0.67 ≦ R ≦ 0.75 to apply and R = 0.70 to 0.75 or R = 0.72. Are particularly advantageous.

  It has diffractive reflection i and diffractive reflection k with half width ≦ 1 °, and at the same time satisfies the relationship of 0.65 ≦ R ≦ 0.85, and sometimes does not show a diffractive reflection whose maximum is 2Θ = 50 ± 0.3 ° The production of the multimetallic oxide material I can be carried out as described in the specifications of DE-A 10118814 and DE-A 10119933.

  At this time, the multi-metal oxide substance I containing a so-called i-phase is important due to the diffraction reflection i. Another crystalline phase that can appear in the multimetal oxide material I is, for example, the so-called k-phase. This is manifested by the presence of diffractive reflections h and k and by the presence of the diffractive reflection with the highest position at 50 ± 0.3 °.

  The intended process for the preparation of the multi-metal oxide material I in which the components of the i-phase to be used according to the invention are dominant is, for example, JP-A11-43314, DE-A10118814, DE-A101199933 and the previous application DE -A10046672 is published in which important multi-metal oxide materials I are used as catalysts for heterogeneously catalyzed oxide hydrogenation from ethane to ethylene and from propane or propene to acrylic acid. It is recommended as a catalyst for gas phase oxidation of heterogeneous catalysts.

  Thereafter, in a manner known per se published in most cited state of the art specifications (for example, also described in the previous application DE-A10033121), first the i-phase and other A multi-metal oxide material of formula (I) that is a mixture of phases (eg, k-phase) is produced. Here, in this mixture, the components of the i-phase are enhanced, for example by selecting another phase, for example the k-phase under the microscope, or by washing the multimetal oxide active with a suitable liquid. I can do it. Examples of such liquids include organic acids (eg, oxalic acid, formic acid, acetic acid, citric acid and tartaric acid), aqueous solutions of inorganic acids (eg, nitric acid), alcohols and aqueous hydrogen peroxide solutions. Furthermore, JP-A 7-23201 also discloses a process for the production of the multi-metal oxide material I to be used according to the invention having an excellent i-phase component.

  The multi-metal oxide material I having an excellent i-layer component to be used according to the invention is obtained in a few systematic ways by the process published in DE-A 19835247. Thereafter, a suitably finely mixed, preferably fine, dry mixture is produced from a suitable source of the elemental components and heat-treated at a temperature of 350 to 700 ° C. or 400 to 650 ° C. or 400 to 600 ° C. . In principle, the heat treatment can be carried out under oxidation or reduction or in an inert atmosphere. Examples of the oxidizing atmosphere include air, air enriched with molecular oxygen, and air enriched with oxygen. The heat treatment is advantageously carried out under an inert atmosphere, ie for example under molecular nitrogen and / or noble gas. The heat treatment is usually performed at a standard pressure (1 atm). Naturally, the heat treatment can be performed under vacuum or super-pressure.

  When the heat treatment is performed in a gaseous atmosphere, it may be stagnant or flowing. The heat treatment may take up to 24 hours or more in total.

  The heat treatment is first advantageously performed at a temperature of 150-400 ° C. or 250-350 ° C. in an oxidizing (oxygen-containing) atmosphere (eg in air). Subsequently, the heat treatment is continued at a temperature of 350 to 700 ° C. or 400 to 650 ° C. or 400 to 600 ° C., preferably under an inert gas. Of course, the heat treatment first tablets the catalyst precursor (possibly after pulverization) before the heat treatment (optionally with addition of 0.5-2% by weight of fine graphite), then heat treatment, followed by It can also be carried out by crushing again.

  Good mixing of the starting compounds within the scope of the production of the multimetal oxide material I to be used according to the invention can be carried out quite generally in a dryer or wet.

  When carried out dry, the starting compound is preferably used as fine and is calcined (heat treated) after mixing and optionally thickening.

  However, it is advantageous to perform good mixing wet. In this case, the starting compounds are usually mixed with one another in the form of an aqueous solution and / or suspension. Subsequently, the aqueous material is dried and calcined after drying. The aqueous substance is preferably an aqueous solution or an aqueous suspension. The drying step is carried out immediately after the preparation of the aqueous mixture, in particular when the aqueous substance to be spray-dried is an aqueous solution, particularly by spray drying, subject to a well-mixed dry mixture (discharge temperature is typically 100 to 150). The spray drying may be carried out by direct current or countercurrent).

  In the scope of the production of the multi-metal oxide material I to be used according to the invention, it is possible to produce oxides and / or hydroxides on heating (possibly in air) as a source of elemental components. This is all that can be done. Of course, as such starting compounds, oxides and / or hydroxides of elemental components can already be used together or subsequently used.

  Sources of elemental Mo used according to the present invention are, for example, molybdenum oxides such as molybdenum trioxide, molybdates such as ammonium heptamolybdate tetrahydrate and molybdenum halides such as molybdenum chloride.

Suitable starting compounds of element V that can be used according to the invention are, for example, vanadyl acetylacetonate, vanadate, such as ammonium metavanadate, vanadium oxide, such as vanadium pentoxide (V ₂ O ₅ ), vanadium halides, e.g., vanadium tetrachloride (CCl ₄₎ and vanadium oxy halides, such as VOCl _3. In this case, a vanadium starting compound containing vanadium with an oxidation degree of +4 can be used in combination.

As a source of elemental tellurium, tellurium oxides such as tellurium dioxide, metal tellurium, tellurium halides such as TeCl ₂ are preferred according to the invention, but telluric acids such as orthotelluric acid H ₆ TeO ₆ are also suitable.

Preferred antimony starting compounds are antimony halides such as SbCl ₃ , antimony oxides such as antimony trioxide (Sb ₂ O ₃ ), antimonic acids such as HSb (OH) ₆ , but antimony oxides— Also advantageous are salts, for example sulfide-antimony oxide (SbO) ₂ SO ₄ .

Niobium sources suitable according to the invention are, for example, niobium oxides such as niobium pentoxide (Nb ₂ O ₅ ), niobium oxide halides such as NbOCl ₃ , niobium halides such as NbCl ₅ , but niobium and organic carboxylic acids. Also suitable are complex compounds consisting of acids and / or dicarboxylic acids, such as oxalates and alcoholates. Of course, the Nb-containing solution used in EP-A 895809 as a niobium source also corresponds to this.

With respect to all other possible elements M ² , the halogenide, nitrate, formate, oxalate, acetate, carbonate and / or hydroxide are particularly suitable as starting compounds according to the invention. . Suitable starting compounds vary and are their oxo compounds, such as tungstates or acids derived therefrom. Ammonium salts are often used as starting compounds.

  Furthermore, as starting compounds for the production of the multimetal oxide material I according to the invention, Anderson Typ polyanions, as described, for example, in Polyhedron Vol. 6, No. 2, pp. 213-218 This is also the case. Another suitable literature source for Anderson polyanions is Kinetics and Catalysis, Vol. 40, No. 3, 1999, pp 401-404.

  Other polyanions suitable as starting compounds are, for example, those of the Dawson or Keggin Typ. Type. According to the invention, at elevated temperatures, starting compounds are advantageously used which are converted to their oxides in the presence of oxygen or by shutting off oxygen, optionally with the liberation of gaseous compounds.

  The multi-metal oxide material I to be used according to the invention obtained as described above is itself [for example as a powder or tableting of powder (often with addition of 0.5-2% by weight of fine graphite). And then crushed into fragments after crushing] or similarly formed into a compact and used in the method according to the invention.

  Molding into a shaped body can be carried out, for example, by coating on a carrier as described in the previous application DE-A 10051419.

  The support to be used for the multimetal oxide material I to be used according to the invention is preferably chemically inert. That is, it does not actually work during the course of catalytic gas phase oxidation of propane to acrylic acid catalyzed by the multi-metal oxide material to be used according to the present invention.

  As support materials, in particular according to the invention, aluminum oxide, silicon dioxide, silicates, such as clay, kaolin, steatite, pumice, aluminum silicate and magnesium silicate, silicon carbide, zircon dioxide and thorium dioxide are relevant.

  The surface of the carrier may be smooth or rough. Since the increased surface roughness is usually predicated on the increased adhesive strength of the coated active substance shell, it is advantageous that the surface of the support is rough.

The surface roughness R _Z of the support is often in the range of 5 to 200 μm and frequently in the range of 20 to 100 μm (using “Hommel Tester Fuer DIN-ISO Oberflaechenmessgroessen” by Fa. Hommelwerke, DE, DIN 4768 Blatt 1).

  Furthermore, the support material may be perforated or non-porous. The support material is advantageously nonporous (total volume of pores ≦ 1% by volume relative to the volume of the support).

  The thickness of the active oxide material shell on the shell-type catalyst according to the invention is typically 10 to 1000 μm. However, it may be 50-700 μm, 100-600 μm or 150-400 μm. Possible shell thicknesses are likewise 10 to 500 μm, 100 to 500 μm or 150 to 300 μm.

  For the method according to the invention, in principle any shape of the carrier is considered. Its longest extension is typically 1-10 mm. However, spherical, cylindrical, and in particular hollow cylindrical materials are advantageously used as the carrier. The preferred diameter of the spherical carrier is 1.5 to 4 mm. When a cylindrical object is used as the carrier, its length is preferably 2 to 10 mm and its outer diameter is 4 to 10 mm. Furthermore, in the case of an annular object, the wall thickness is typically 1 to 4 mm. An annular carrier suitable according to the invention can have a length of 3-6 mm, an outer diameter of 4-8 mm and a wall thickness of 1-2 mm. However, an annular carrier shape 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) is also possible.

  The production of the shell-type catalyst to be used according to the invention is in the simplest way by pre-generating the active oxide material of the general formula (I), converting it into a fine form, and finally with a liquid binder This can be done by coating it on top. For this purpose, the surface of the support is wetted with a liquid binder in the simplest way and a layer of active substance is deposited on the wet support by contact coating with a finely active oxide material of general formula (I). Finally, the layered carrier is dried. Of course, this process can be repeated periodically to increase the layer thickness. In this case, the layered substrate becomes a new “carrier” or the like.

  The purity of the catalytically active oxide material of general formula (I) to be coated on the surface of the support is of course adapted to the desired shell thickness. In the shell thickness range of 100-500 μm, for example, at least 50% of the total number of powder particles passes through a sieve having a mesh width of 1-20 μm, and the numerical component of particles having the longest extension of 50 μm or more is more than 10%. Less active material powder is preferred. As a rule, the distribution of the longest elongation of the powder particles corresponds to a Gaussian distribution, depending on the production conditions. The particle size distribution is often as follows:

The following represents the following:
D = particle size,
x = percentage of particles whose diameter is ≧ D and y = percentage of particles whose diameter is <D.

  In order to carry out the above-mentioned coating process on an industrial scale, it is recommended to apply the method principle published, for example, in DE-A 2909671 and DE-A 10051419. That is, the support to be coated is advantageously inclined (tilt angles are typically ≧ 1 ° and ≦ 90 °, mostly ≧ 30 ° and ≦ 90 °; the tendency angle is the central axis of the rotating vessel relative to the horizontal In a rotatable rotating container (e.g., rotating plate or layered drum). In the rotating rotating container, for example, a spherical or cylindrical carrier is passed under two supply devices arranged continuously at regular intervals. The first of the two supply devices preferably corresponds to one nozzle (for example a spray nozzle operated with pressure air), through which the rotating carrier in the rotating rotating dish passes through the liquid binder. Is sprayed and adjusted wet. The second supply device is outside the conical spray of the liquid binder to be sprayed and is used to supply fine oxide active material (eg, via a vibrating groove or powder screw). The conditioned wet carrier spheres take in the supplied active substance powder, which is condensed into a dense shell by rotational movement, for example on the outer surface of a cylindrical or spherical carrier.

  If necessary, the base-coated carrier thus passes again through the spray nozzle during the subsequent rotation, in this case taking in another layer of fine oxide active material during further movement. And so on (intermediate drying is usually not necessary). Here, the fine oxide active substance and the liquid binder are usually supplied continuously and simultaneously.

The removal of the liquid binder can be carried out, for example, by the action of a hot gas such as N ₂ or air after the end of the coating. It is notable that the above-mentioned coating method causes a sufficiently satisfactory deposition of the adjacent continuous layers as well as the basic coating on the surface of the support.

  The above-described coating method is essentially performed by a method in which wetting of the surface to be coated of the carrier is adjusted. In short, the surface of the carrier certainly has the liquid binder adsorbed, but the surface of the carrier is advantageously wetted so that the liquid phase does not appear as such on the surface of the carrier. If the support surface is too wet, the fine catalytically active oxide material aggregates into separate agglomerates instead of depositing on the surface. Detailed descriptions in this regard can be found in DE-A 2909671 and DE-A 10051419.

  Can be done by sublimation. In the simplest case, this can be done by the action of hot gas at a corresponding temperature (often 50-300, often 150 ° C.). However, pre-drying can also be caused by the action of hot gas. Final drying can then be performed, for example, in any type of drying oven (eg, a band dryer) or in a reactor. The temperature applied here must not be higher than the calcination temperature applied in the production of the oxide active material. Of course, the drying can also be carried out exclusively in a drying oven.

  Regardless of the type and shape of the carrier, the following can be used as binders in the coating process: water, monohydric alcohols such as ethanol, methanol, propanol and butanol, polyhydric alcohols such as Ethylene glycol, 1,4-butanediol, 1,6-hexanediol or glycerin, mono- or polyvalent organic carboxylic acids such as propionic acid, succinic acid, malonic acid, glutaric acid or maleic acid, amino alcohols such as Ethanolamine or diethanolamine and mono- or polyvalent organic amides such as formamide. Preferred binders are solutions consisting of 20 to 90% of water and 10 to 80% of organic compounds dissolved in water, whose boiling point or sublimation temperature is> 100 ° C., preferably> 150 ° C. at standard pressure (1 atm). is there. From the list of possible organic binders mentioned above, organic compounds are advantageously selected. The organic component of the aqueous binder solution is preferably 10-50, particularly preferably 20-30% by weight. In this case, monosaccharides and oligosaccharides such as glucose, fructose, sucrose or lactose, polyethylene oxide and polyacrylate are applicable as organic components.

  It is important that the production of shell-type catalysts suitable according to the invention can be carried out not only by coating the finished fine active oxide material of general formula (I) on the wet support surface.

  Rather, instead of the active oxide material, the fine precursor itself is coated on the wet carrier surface (using the same coating method and binder) and calcined after drying the coated carrier. You can also

  As such a fine precursor, for example, from the source of the elemental component of the desired active oxide material of the general formula (I), first an advantageously finely mixed, preferably finely dried mixture is produced (for example, 150 to 350 ° C., preferably from 250 to 350 ° C., preferably by spray drying of an aqueous suspension or aqueous solution of the source, this finely dried mixture (optionally after tableting with addition of 0.5 to 2% by weight of fine graphite). This applies to substances obtained by heat treatment (several hours) in an oxidizing (oxygen-containing) atmosphere at a temperature of 350 ° C. (for example in air) and finally pulverizing if necessary.

  After the support has been coated with the precursor, it is preferably calcined at a temperature of 360-700 ° C. or 400-650 ° C. or 400-600 ° C., preferably in an inert gas atmosphere (all other atmospheres are also considered).

  Of course, the formation of the multimetal oxide material I that can be used according to the invention can be carried out by extrusion and / or tableting of both the fine multimetal oxide material I and the fine precursor of the multimetal oxide material I. I can do it.

  In this case, the spherical shape, the complete cylindrical shape, and the hollow cylindrical shape (annular shape) correspond to this. At this time, the longest extension of the shape is usually 1 to 10 mm. In the case of a cylindrical object, the length is preferably 2 to 10 mm, and the outer diameter is preferably 4 to 10 mm. Furthermore, in the case of an annular object, the wall thickness is typically 1 to 4 mm. A ring-shaped complete catalyst suitable according to the present invention can have a length of 3-6 mm, an outer diameter of 4-8 mm, and a wall thickness of 1-2 mm. However, complete catalyst annulus shapes of 7 mm x 3 mm x 4 mm or 5 mm x 3 mm x 2 mm (outer diameter x length x inner diameter) are also possible.

  Of course, all that of DE-A 10101695 is also considered for the shape of the multimetal oxide material I to be used in the process according to the invention.

It is essential according to the invention that the multi-metal oxide material I to be used advantageously according to the invention exhibits a roentgen diffractogram (here, always against Cu-Kα radiation), which is Shows reflections h, i and k, and their vertices at the diffraction angle (2Θ) are 22.2 ± 0.4 ° (h), 27.3 ± 0.4 ° (i) and 28.2 ± 0. 4 ° (k),
Diffraction reflection h is in the strongest X-ray diffraction diagram and shows a half-value width of at most 0.5 °,
The intensity P _i of the diffraction reflection _i and the intensity P _k of the diffraction reflection k satisfy the relationship of 0.65 ≦ R ≦ 0.85, where R is an expression:
R = P _i / (P _i + P _k )
And the half widths of the diffraction reflection i and the diffraction reflection k are each ≦ 1 °.

  The definition of the intensity of the diffracted reflection in the X-ray diffractogram relates to the definitions described in DE-A 19835247 and DE-A 10051419 and DE-A 10046672 in this document.

That is, A ¹ represents the apex of reflection 1 and B ¹ is the closest to the left side of apex A ^{1 when} viewed along the intensity axis standing perpendicular to the 2Θ-axis in the X-ray diffraction line. And B ² represents the most recent lowest value to the right of vertex A ^{1 in} a corresponding manner, and C ¹ is the corresponding lowest value. , A straight line drawn perpendicularly from the vertex A ¹ to the 2Θ-axis represents a point intersecting with a straight line connecting the points B ¹ and B ² , and at this time, the intensity of the reflection 1 extends from the vertex A ¹ to the point C ^1. This is the length of the straight line segment A ¹ C ¹ . In this case, the expression “minimum value” means a point where the rising gradient of the tangent line placed on the curve in the basic range of reflection 1 shifts from a negative value to a positive value, or a point where the rising gradient goes to zero. For the determination of the ascending slope, the coordinates of the 2Θ axis and the intensity axis are cited.

In the present specification, the half-width is determined in a corresponding manner by a straight line segment between ^two intersections H ¹ and H ² when a parallel line to the 2Θ-axis is drawn at the center of the straight line segment A ¹ C ¹ . Length, where H ¹ , H ² mean the first intersection of each of the above defined straight lines of the X-ray diffraction diagram and this parallel line on the left and right sides of A ¹ .

  An exemplary implementation of half width and intensity measurements also shows FIG. 6 in DE-A 10046672.

The X-ray diffraction diagram of the multi-metal oxide material I to be used according to the invention preferably shows, in addition to the diffracted reflections h, i and k, other diffractive reflections whose vertex is usually the next diffraction angle (2Θ). Have:
9.0 ± 0.4 ° (l),
6.7 ± 0.4 ° (o) and 7.9 ± 0.4 ° (p).

The X-ray diffractogram of the catalytically active oxide material of the general formula (I) advantageously contains additionally a diffraction angle whose vertex is the following diffraction angle (2Θ):
45.2 ± 0.4 ° (q).

  Often, the X-ray diffraction pattern of the multi-metal oxide material (I) also has reflections of 29.2 ± 0.4 ° (m) and 35.4 ± 0.4 ° (n).

If the catalytically active oxide material of general formula (I) has a k-phase, its X-ray diffractogram usually has another diffractive reflection whose vertex is the next diffraction angle (2Θ):
36.2 ± 0.4 ° and 50.0 ± 0.4 °.

When adding an intensity of 100 to the diffraction angle h, according to the invention, it is advantageous if the diffraction angles i, l, m, n, o, p, q show the following intensities on the same intensity scale:
i: 5-95, often 5-80, partially 10-60;
l: 1-30;
m: 1-40;
n: 1-40;
o: 1-30;
p: 1-30 and q: 5-60.

  If the X-ray diffractogram has an additional diffraction reflection, its half-value width is typically ≦ 1 °.

  In this specification, all data relating to X-ray diffractograms relate to X-ray diffractograms that occur under the use of Cu-Kα-radiation as X-ray radiation (Siemens-Diffraktometer Theta-Theta D-5000, vacuum tube voltage: 40 kV, vacuum tube Current: 40 mA, aperture stop V20 (variable), scattering radiation stop V20 (variable), secondary monochromator stop (0.1 mm), detector stop (0.6 mm), measurement interval (2Θ): 0. 02 °, measurement time of each step 2.4 s, detector: scintillation counter).

The specific surface area of the multimetal oxide material (I) to be used according to the invention is often 1-30 m ² / g (BET-surface area, nitrogen).

  The catalyst to be used according to the invention, which is newly produced in the process according to the invention, preferably has firstly a reaction gas having an increased water vapor component (ie in composition range A) relative to the propane contained. Exposed to the starting mixture.

  When the process according to the invention is applied as solid bed oxidation, it is an advantageous process and is carried out in a bundle reactor with a catalyst in its contact tube. Usually, a liquid, usually a salt bath, is induced around the contact tube as a heat transfer body.

  The reaction gas mixture is directed in a contact tube, either directly or countercurrently to the salt bath, as viewed from the whole reactor. The salt bath itself can flow relatively completely in parallel with the contact tube. However, of course, this can also overlap the cross current. Overall, the salt bath can also flow in a meandering manner around the contact tube, and this flow may be directed in direct or countercurrent to the reaction gas mixture if only the reactor is viewed. Suitable bundle reactors for the process according to the invention are published, for example, in the specifications EP-A 700714 and EP-A 700893. In the process according to the invention, the loading of the catalyst loading with propane may be, for example, 10 to 500 Nl / l · h. The loading with the reaction gas starting mixture is often in the range of 100 to 10000 Nl / l · h, often in the range of 500 to 5000 Nl / l · h.

  In the process according to the invention, the reaction gas starting mixture may be preheated to the reaction temperature and fed to the reaction zone containing the catalyst.

Of course, the process according to the invention gives a product gas mixture which does not necessarily consist exclusively of acrylic acid. Rather, the product gas mixture, in addition to the unreacted propane, secondary components, for example, contains propene, _{acrolein, CO 2, CO, H 2} O, acetic acid, propionic acid and the like, acrylic acid from them must be separated .

  This separation is known for heterogeneously catalyzed gas phase oxidation of propene to acrylic acid because the process according to the invention limits the amount of water vapor contained in the product gas mixture as well as the by-product formation of acetic acid and propionic acid. Can be done.

  That is, the containing acrylic acid contains from the product gas mixture, for example, a high boiling inert hydrophobic organic solvent (eg, a mixture comprising diphenyl ether and diphenyl, which optionally further contains an additive, eg, dimethyl phthalate). Can be extracted by adsorption. The adsorbent and acrylic acid mixture remaining there can subsequently be finished to pure acrylic acid by rectification, extraction and / or crystallization in a manner known per se. Alternatively, the radical separation of acrylic acid from the product gas mixture can also be carried out by fractional condensation, for example as described in DE-A 19924532.

  The acrylic acid condensate remaining here can then be further purified, for example, by fractional crystallization (eg suspension crystallization and / or layered crystallization).

  The residual gas mixture remaining during the radical separation of acrylic acid contains in particular unreacted propane and optionally unreacted propene. This can be separated from the residual gas mixture, for example by fractional pressure rectification, and subsequently returned to the gas phase oxidation according to the invention. However, it is more advantageous to contact the residual gas in the extraction device with a hydrophobic organic solvent that can adsorb propane and possibly propene, for example, by passing it through.

  Subsequent desorption and / or stripping in air allows the adsorbed propane and possibly propene to be liberated again and returned to the process according to the invention. In this way, an economical total propane conversion can be achieved. Of course, however, acrylic acid can also be separated from the product gas mixture by the method described in DE-A10059122.

  It is noteworthy that the process according to the invention allows a high selectivity of acrylic acid production with a reduced water vapor requirement.

  Of course, the multi-metal oxide material I to be used according to the invention is a fine, for example colloidal material, diluted in a form diluted with, for example, silicon dioxide, titanium dioxide, aluminum oxide, zircon oxide and niobium oxide. It can be used in the method according to the invention.

  At this time, the dilution substance ratio may be up to 9 (diluent): 1 (active substance). That is, possible diluent substance ratios are, for example, 6 (diluent): 1 (active substance) and 3 (diluent): 1 (active substance). Diluent admixture can occur before and / or after calcination. If additive mixing is performed prior to calcination, the diluent must be selected so that it remains in effect during calcination. This is the case for example in the case of oxides combusted at correspondingly high temperatures.

  The catalyst used in the process according to the invention is regenerated many times at temperature ≦ reaction temperature by the introduction of an oxygen-containing gas to which water vapor may be added, for example air or oxygen-poor or enriched air. obtain.

Example
A) Production of the multimetal oxide-I-catalyst to be used according to the invention Ammonium metavanadate (V ₂ O ₅ 77.5) in 44.6 l of water at 80 ° C. with stirring in a refined steel vessel (Mass%, Fa.GfE, DE-Nuernberg) 1287.25 g was dissolved. A clear yellowish solution was formed. The solution is allowed to cool to 60 ° C. and then, in succession, in the above order, firstly 1683.75 g of telluric acid (H ₆ TeO ₆ 99% by weight, Fa. Fluka) and then heptamolybdenum while being held at 60 ° C. Ammonium acid (MoO ₃ 81.5 mass%, Fa. Starck) 5868.0 g was mixed and stirred. A deep red solution A was formed. In a second refined steel container, 1599.0 g of ammonium niobium oxalate (Nb 21.1% by mass, Fa. Starck, DE-Goslar) was dissolved in 8.3 l of water at 60 ° C. to obtain a solution B. The two solutions A and B were allowed to cool to 30 ° C. and merged together at this temperature, with solution B being mixed and stirred into solution A. The mixing and stirring was continuously performed within 10 minutes. An orange aqueous suspension was formed.

This suspension was subsequently spray dried (T _receptor = 30 ° C., T ^entry = 240 ° C., T ^entry = 110 ° C., drying time: 1.5 hours, Fa. Nipolosa spray tower). The spray material obtained was likewise orange. In this spray material, fine graphite (sieving analysis: minimum 50% by weight <24 μm, maximum 10% by weight> 24 μm and <48 μm, maximum 5% by weight> 48 μm, BET-surface area: 6-13 m ² / g) 1% by weight Were mixed.

  The resulting mixture is compressed (pressurized) into a hollow cylinder (annular material) having a shape of 16 mm × 2.5 mm × 8 mm (outer diameter × height × inner diameter). I was there.

200 g of the annular material was calcined in a rotating spherical furnace according to FIG. 1 in order at 100 g in two portions (1 liter quartz glass spherical furnace; 1 = furnace vessel, 2 = rotary flask, 3 = heating chamber, 4 = nitrogen- / air flow). For this purpose, the rotary spherical furnace contents are heated from 25 ° C. to 275 ° C. within 27.5 minutes with a linear heating gradient under a flow of 50 Nl / h of air and at this temperature, the air flow is kept constant. Hold for 1 hour. Subsequently, within 32.5 minutes, a linear heating gradient was used to heat from 275 ° C. to 600 ° C., with the air flow being changed to a nitrogen flow of 50 Nl / l. The 600 ° C. and nitrogen flow was held for 2 hours, and then all furnaces were allowed to cool to 25 ° C. under nitrogen flow hold by themselves. A black tablet of the composition Mo _1.0 V _0.33 Te _0.15 Nb _0.11 O _x was produced.

The tablets were dried and ground to a particle size <100 μm in a Retsch-mill. 150 g of the pulverized material was reflux-stirred in 1500 ml of a 10% by weight HNO ₃ -water solution for 7 hours at 70 ° C., and the solid was collected from the resulting suspension by filtration and washed with water to remove nitrates. The filter cake was dried overnight at 110 ° C. in air in a muffle furnace. The resulting active material had the composition Mo _1.0 V _0.27 Te _0.12 Nb _0.13 O _x .

75 g of the active substance powder thus obtained was added to a spherical carrier having a diameter of 2.2 to 3.2 mm (carrier material = Fa. Ceramtec, DE steatite, carrier pore total volume ≦ 1% by volume relative to the carrier total volume; R _z = 45 μm ) Over 300g. For this purpose, the carrier was preloaded in a coated drum with a volume of 21 (inclination angle of the drum central axis with respect to the horizontal = 30 °). The drum was rotated at 25 revolutions per minute. About 30 ml of a mixture of glycerin and water (mass ratio glycerin: water = 1: 3) was sprayed on the support over a period of 60 minutes via a spray nozzle operated with pressurized air 300 Nl / h. At this time, the nozzle was installed so that the sprayed spherical material wets the carrier carried to the uppermost point of the inclined drum by the rotating plate in the drum in the upper half of the falling section. The active substance fine powder was charged into the drum by means of a powder screw, the powder feed point being within the tumbling section, but at the bottom of the spray sphere. Due to the periodic repetition of wetting and powder dispensing, the fundamentally coated carrier became the carrier itself in subsequent cycles.

After the end of coating, the coated carrier was dried for 16 hours at 120 ° C. in a circulating air drying oven (Firma Binder, DE, content 53 l). The glycerin was removed in air at 150 ° C. by a subsequent 2 hour heat treatment. A shell-type catalyst S having 20% by mass of the active substance component to be used according to the present invention was obtained.
B) Implementation of the method according to the invention and the comparative method 35 g of the newly produced shell-type catalyst S were each placed in a single-tube reactor heated by an electric heating mat (tube length: 140 cm, inner diameter: 8.5 mm, outer Diameter: 60 mm, V2A steel, catalyst bulk length: 54.5 cm, in addition to preheating the reaction gas starting mixture, 30 cm length consisting of Fa. Ceramtec steatite spheres (diameter 2.2-3.2 mm) And the reaction tube was filled with the same steatite spheres after the end of the catalyst zone). The shell type catalyst was placed in a tubular reactor in air at a mat temperature of 350 ° C.

Thereafter, in four unrelated tests W, X, Y and Z, four new tubular reactor catalyst charges were added to the next reaction gas starting mixture W at a heating mat temperature of 50 ° C. for 48 hours. Coated with X, Y and Z:
W: Propane 3.3 volume%, O ₂ 10 volume%, N ₂ 40 volume%, H ₂ O 46.7 volume%
X: Propane 3.3 volume%, O ₂ 10 volume%, N ₂ 40 volume%, H ₂ O 46.7 volume%
Y: Propane 3.3% by volume, O ₂ 10 vol%, N ₂ 70 vol%, H ₂ O 16.7% by volume
Z: Propane 3.3% by volume, O ₂ 10 vol%, N ₂ 86.7% by volume, H ₂ O 0 volume%.

  The residence time (relative to the catalyst bulk capacity) was 2.4 seconds in all cases. The operating pressure was 2 bar absolute in all cases.

At the end of 48 hours, the reaction tube was further charged with the next reaction gas starting mixture composition while maintaining the residence time, with the following result (passing through a single reaction tube) after a further 4 hours of operation. Was achieved (T _M = applied heating mat temperature):
W (according to the invention): propane 3.3% by volume, O ₂ 10% by volume, N ₂ 86.7% by volume, H ₂ O 0% by volume,
T _M = 390 ° C.
Propane conversion rate in one reaction tube ( _UP ): 25 mol%,
Selectivity (S _AS ) of acrylic acid production in one reaction tube passage: 50 mol%.
Z (compared to W): propane 3.3% by volume, O ₂ 10% by volume, N ₂ 86.7% by volume, H ₂ O 0% by volume,
T _M = 390 ° C.
U _P = 25 mol%,
S _AS = 40 mol%.
X (according to the invention): propane 3.3% by volume, O ₂ 10% by volume, N ₂ 70% by volume, H ₂ O 16.7% by volume,
T _M = 370 ° C.
U _P = 25 mol%,
S _AS = 70 mol%.
Y (compared to X): propane 3.3% by volume, O ₂ 10% by volume, N ₂ 70% by volume, H ₂ O 16.7% by volume,
T _M = 385 ° C.
U _P = 25 mol%,
S _AS = 50 mol%.

  The results achieved show the advantages of the method according to the invention.

1 schematically shows a rotating spherical furnace for carrying out the process according to the invention for acrylic acid by heterogeneous catalytic partial oxidation of propane.

Claims (4)

In a process for producing acrylic acid by heterogeneous catalytic partial oxidation of propane in the gas phase, a reaction gas starting material containing a diluent gas comprising propane, molecular oxygen and water vapor is heated at elevated temperature to a general chemical formula I:

[Where:
M ¹ represents Te and / or Sb,
M ² is, Nb, Ta, W, Ti , Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, La, Bi, B, Ce, Sn, Zn, Si and Represents at least one element from the group comprising In;
b is 0.01-1;
c is> 0 to 1,
where d is> 0 to 1 and n is a number determined by the valence and power of an element different from oxygen in (I)], wherein In the partial oxidation of propane to acrylic acid, the composition of the reaction gas mixture is changed at least once during the performance of the process, and in the reaction gas starting mixture, the molar amount of propane contained in the reaction gas starting mixture. On the other hand, the amount of the diluted gas water vapor contained before the change is smaller after the change, and the acrylic acid by the heterogeneous partial oxidation of propane in the gas phase is characterized in that How to manufacture . In the reaction gas starting mixture, before changing its composition, the following molar ratio:
Propane: Oxygen: H ₂ O: Other dilution gas = 1: (0.1-10): (0.1-50): (0-50)
The method of claim 1, wherein: In the reaction gas starting mixture, after changing its composition, the following molar ratio:
Propane: Oxygen: H ₂ O: Other dilution gas = 1: (0.1-10): (0-30): (0-30)
The method of claim 1, wherein:   The process according to any one of claims 1 to 3, wherein the reaction temperature is 250 to 550 ° C before changing the composition of the reaction gas starting mixture.

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